The present invention relates generally to an air conditioner for a vehicle, and more particularly to an air conditioner for a vehicle capable of automatically regulating an inside air temperature in a vehicle compartment to a preset temperature as desired by a vehicle occupant.
Due to large thermal loads on an air conditioner cooling system mounted in a vehicle, differences between the inside space air temperature (inside air temperature) and internal surface temperature of the vehicle compartment (e.g., internal surface temperature of window glass) cause heating. Also, solar radiation may heat the vehicle compartment. The temperature of the internal surface of the vehicle compartment, related to this heating, is influenced by the external surface temperature of the vehicle (e.g., external surface temperature of window glass). The temperature of the external surface of the vehicle is also influenced by outside air temperature and solar radiation.
Therefore, a conventional air conditioner for a vehicle is equipped with an inside air temperature sensor for detecting inside air temperature, an outside air temperature sensor for detecting outside air temperature and a solar radiation sensor for detecting an intensity level of solar radiation. In this arrangement, the thermal load is estimated indirectly according to signals supplied from these sensors, and a level of the latter thermal load is estimated using a solar radiation intensity level detected by the solar radiation sensor. Based on the thermal load levels thus estimated, calculations are performed to attain a target value of a blowout air temperature (target blowout air temperature), a control target voltage for an air blower, etc.
Further, in a conventional air conditioner for a vehicle disclosed in JP-A-10-230728 or JP-A-10-197348, infrared ray sensors (surface temperature sensors) arranged in a matrix form are used instead of the above inside air temperature sensor and solar radiation sensor to detect a surface temperature of a vehicle occupant. According to temperature signals from these infrared ray sensors, ambient temperature and a solar radiation intensity level is estimated in the vicinity of the vehicle occupant.
However, in this system, an estimated thermal load may not meet an actual thermal load in some cases. As such, accurate interior temperature control cannot be attained. Further, in the latter conventional air conditioner, a thermal load is estimated indirectly according to a solar radiation intensity level estimated from the surface temperature of the vehicle occupant. This creates the same problem as in the former conventional air conditioner for a vehicle.